Hey, if the names they get are the last things they remember of their past lives, thus saying it once conscious on the other side, maybe Trilby and Fedora killed each other in a stand off, hence the name mixup.

Puns. I have to call a different skeleton now, then.
*Calls someone on cell phone*
*You hear Megalovania playing in the distance, getting louder by the second. It suddenly gets extremely loud without warning.
Other Skeleton: So, you think that you’re SANSational at puns, eh?
(Ahh, Undertale references! ;3)